1. Field of the Invention
The present invention relates to an optical pickup used when reading information recorded on an optical disk and writing information to an optical disk.
2. Description of Related Art
There are known in the prior art optical pickups capable of reading and writing information from and to Blu-Ray discs (“BDs”), digital versatile discs (“DVDs”), and compact discs (“CDs”).
Some of these optical pickups are compatible with a plurality of types of optical disks such as BD, DVD, and CD using a single objective lens, as described in, e.g., Japanese Patent Application No. 2009-70545. Other optical pickups are provided with two types of objective lenses (e.g., a BD objective lens, and a DVD and CD objective lens) that are interchangeably used depending on the type of optical disk, as described in, e.g., Japanese Patent Application No. 2009-116937.
The objective lens referred to herein is a lens for focusing light emitted from a light source onto an information recording surface of an optical disk.
The use of a single objective lens is advantageous in terms of allowing the optical pickup to be made more compact, among other benefits. Over the past several years, techniques for fabricating objective lenses from plastic have been improved so that it is now possible to manufacture objective lenses configured so as to be capable of minimizing spherical aberration (lenses having a diffractive structure) even for use in BDs, DVDs, or CDs. In view of the above, there are rising expectations in the market for an optical pickup that is compatible with a plurality of types of optical disks such as BDs, DVDs, and CDs using a single objective lens.